1. Field of the Invention
The present invention relates to a process for the preparation of stable graft copolymer dispersions of low viscosity and superior particle size distribution. More particularly, the invention relates to the in situ polymerization at a temperature below 100.degree.C. of vinyl monomers in a co-reactive unsaturation-containing polyol in the presence of a free radical catalyst and a chain transferring agent.
2. Prior Art
Graft copolymer dispersions prepared from vinyl monomers and unsaturation-containing polyether polyols and the use thereof in the preparation of polyurethane polymers are well known in the art as evidenced by U.S. Pat. No. 3,652,659 as well as British Pat. No. 1,063,222. These patents disclose various methods of preparing graft copolymer dispersions. All of the patents relate to the problem of high viscosities. As a general rule, in order to obtain efficient grafting in the presence of free-radical catalysts, the in situ polymerization is carried out at temperatures between 100.degree.C.-130.degree.C. and employing high (over 2% by weight of the vinyl monomers) concentration of catalyst. These high temperatures do considerable damage to sensitive monomers such as acrylonitrile and vinylidene chloride as well as to the polyols, resulting in colored dispersions. The present invention relates to an improvement in the preparation of graft copolymer dispersions prepared in unsaturation-containing polyols.